This one somehow manages to be fun whilst not actually explaining itself in the slightest. The aliens are doing something, but we don't really know what. They're after something, but they're at pains not to tell us what it is, presumably so the writers don't have to bother to think it up; and there's lots of running about for pretty much no reason whatsoever. I didn't get bored at all though, as I did in some of the other uneventful episodes. Pointless, then, but reasonably engagingly so.

An alien telephone engineer, up a pole. It's snowing, as it will be doing for most of the rest of the episode. For much of the time the cast looks absolutely freezing.

Another alien telephone engineer, this time in a mysterious van. He is doing mysterious van things.

This is the mysterious van equipment with which he is doing the mysterious van things, in the mysterious van. It has a glowing crystal on it, which is nice.

Whilst in full glow it causes telephones to melt, which can only ever be a good thing.

And it also causes telephone boxes to explode, which is entertaining, if probably rather less so for the man who was in there at the time making a call.

I have no idea why the telephone box blew up, but the home phone only melted. This is the sort of strange discrepancy that aliens probably hope they won't get asked about.

Some homeless people. Shortly afterwards, the woman sees the man taken over by an alien, and runs away in terror. She then gets taken to a mental home. Why, I have no idea, as she is in no way mad, nor acting it.

Still, it does give her the opportunity to meet Sylvia, although she'd probably have been better off if she hadn't bothered.

Elsewhere, Ironhorse is wrestling with new recruits, tasked with breaking into the safe house without him noticing - somewhat unfair, I'd have thought, since presumably he's waiting for them to sneak in. Anyway, they wrestle.

Ironhorse is concerned, because the selection process has left him with a female recruit, and he is not at all sure that a woman can be trusted to do army things. However presumably he's going to be enjoying wrestling her to find out.

Downstairs, Harrison and Norton grumble about telephones not working. Either because they're deeply paranoid, or just because they understand the rules of television, they immediately assume that aliens are involved.

Some aliens, being involved. They've taken over some homeless people, on the grounds that they won't be missed. You know, I suspect that there may have been a social comment somewhere in the original script, that's been somewhat swept under the carpet. Anyway, the aliens are at a truck stop, looking for a truck that contains a "power source" that they need to steal. It will power their strike against the telephone system, so as to render humanity unable to communicate. What the power source is, where it comes from, what it does, and what they're hoping to use it to power are all questions that we're unlikely ever to have answered.

Meanwhile, Sylvia and the homeless woman have run away together, because the hospital staff refuse to believe their stories about aliens, or to call Harrison. Since Harrison has thoughtfully squirreled himself away in a secret, underground hideout, and not told her where it is, Sylvia presumably figures that she'll investigate things herself. Or she just plans on running about and squealing; whichever will help the least.

Ironhorse, meanwhile, is running laps of the garden with his new recruits. Endlessly, for much of the episode.

Harrison receives news that Sylvia has run away from her nursing home; or more likely from the ghastly staff. Ironhorse is still busy running laps of the insanely large back garden, so this is the perfect time for sneaking out of the house.

Harrison has the biggest coat ever. Suzanne has a very silly hat. Together they are therefore perfectly equipped for scouring an unknown city in search of one lone woman.

They begin to ask random passers-by if they happen to have seen any redheads called Sylvia at all lately.

None of them have.

Suzanne seems more afraid of that man's hair than she ever has been of any alien.

Ironhorse does a bit more jogging with the recruits.

Whilst Harrison, having got nowhere, worries about Sylvia as darkness falls. Sylvia is fine, though. Her homeless friend knows all the best places to shelter, and has taken her to a truck stop where there are some good places to sleep. And yes, that would be the same truck stop where the aliens have all gone.

Sylvia sees her new friend get taken over by the aliens.

The unfortunate thing about being an alien is that you're not supposed to notice the cold anymore. So you have to take off your nice warm hat, despite the fact that you're clearly filming in sub-Arctic temperatures.

Anyway, the aliens now have possession of all the information that the homeless woman had in her brain, including everything that Sylvia told her about Harrison. This leads to a brilliantly continuity-busting scene where they mutter about a human who knows all about them! Oh no! He must be stopped! Despite the fact that they've known of him for at least half a season, and have even tried to infiltrate his team with a Trojan dolphin scientist, just to get at him. But never mind.

Sylvia panics and flees.

Having heard that the truck stop is a good place to look for homeless people, Harrison and Suzanne go there. They fail to find Sylvia from their vantage point of sitting in their truck and not bothering to look for her at all.

Moments later she hurtles by them in a panic, which is convenient. Harrison snags her, and she babbles out her story. So, once again Harrison has set out into the great wide world without support or a plan, and has wound up surrounded by aliens. You'd think a genius scientist would have spotted the pattern by now.

He calls home on his fabulous mobile phone, to report success on the Sylvia front; and rather less success on the staying out of trouble and not getting murdered to death by hordes of alien soldiers front.

Norton, who has (to his great surprise, for some reason) tracked some alien transmissions to the same location, reports that Ironhorse is already on his way. He suggests staying out of trouble in the meantime. Ha.

Harrison and co watch the aliens creep about the place. They spot a homeless man heading straight towards a group of them, and realise that he's about to get himself killed. Harrison groans and says "I hate it when this happens," as though he spends his entire life hurtling to the rescue of stray homeless people, who are about to wander into deadly alien enclaves. Still, I suppose it's possible. Presumably the TV show doesn't chronicle his every waking moment.

Anyway, he hurtles to the rescue, only to find that the homeless man is Ironhorse in disguise. They wrestle for a bit.

Then, having identified each other, they wrestle some more, because there's nothing much else going on, and plenty of time to waste.

Having made it back upright, they watch aliens creeping out, being alieny. Ironhorse rallies his troops.

Fighting aliens is srs bsns.

There's an explosion. I have no idea why. A recruit fires a gun, an alien falls over, and boom. Not that I'm complaining. It's a very nice boom, and they're always appreciated. If the aliens have suddenly turned explosive, though, I feel we should have been told.

Ironhorse's new crack troops. I'm not terribly encouraged by their presence.

Meanwhile, Sylvia's aliened friend homes in on Harrison, because he knows about the aliens, and must be destroyed. I can only assume it's one of the slower aliens who has possessed her, or one who was ill, and missed the Harrison Blackwood briefing six months ago. Anyway, she's shot dead - by the new female recruit; so you see, women are okay in the army after all. That's nice. Then they all go home.

A confusing episode this. There are clearly two storylines here that have been jammed together for some reason. Somebody has written an episode about aliens taking over homeless people, because they won't be missed. Nice idea. Somebody else has then come up with an episode about cutting off human communications, which again is a nice idea; but stapling them together only results in two half ideas that don't go anywhere. I can't help thinking it would have been better to have expanded them into two separate episodes. It's one that could be fun in a remake, though. Instead of the aliens doing something weird with phones, they could mess with the internet. That could be really good. Provided it did actually go somewhere, rather than just being about hiding in a truck stop for half an hour, and hissing about that pesky Harrison Blackwood.